Macro- and microstructure analysis and mechanical characteristics of thick AlMg5 alloy plates joined by floating-bobbin friction stir welding

摘要

The present paper explores the simultaneous influence of rotational and traverse speeds on the macrostructure, microstructure, and mechanical characteristics of welds produced by the floating-bobbin friction stir welding of 20-mm-thick AlMg5 alloy plates. The macrostructure results revealed that the visual quality of the welds was reduced with an increase in the rotational speed due to the waste of plasticized material and the formation of excessive flash. Also, with increasing the rotational speed and reducing the traverse speed, increases happened in the joint width in the central zone, the recrystallized grains size at the upper, middle and lower layers of the stir zone, and the difference between them due to the increased heat input. However, the heat input of the process was distributed across a greater volume of the base metal in these conditions, and the hardness at all three layers of the stir zone decreased. The tensile properties of the welds decreased with an increase in the rotational speed and a decrease in the traverse speed due to the formation of defects in the welding zone. The best tensile strength was almost 314 MPa obtained under a rotational speed of 90 rpm and a traverse speed of 40 mm/min, and its fracture location was adjacent to the base metal with the heat-affected zone. The fracture surface has different characteristics at the upper, middle and lower layers, and the dimples on the upper and lower layers are always coarser and deeper than those occurring on the middle layer.